Motion picture print films, the film that is shown in movie theaters, commonly employ optical soundtracks along at least one edge of the film. The most common optical soundtracks presently in use are analog soundtracks of the "variable area" type wherein signals are recorded in the form of a varying ratio of opaque to relatively clear area along the soundtrack. During projection of the motion picture images, a light source illuminates the soundtrack and a photosensor senses the light passing through and modulated by the soundtrack to produce an audio signal that is sent to amplifiers of the theater sound system.
Digital soundtracks for motion picture films have been more recently introduced, wherein sound information is recorded in a digital format, e.g. comprising small data bit patterns on the film, typically between perforations of the motion picture film (e.g., Dolby.TM. Digital Stereo soundtracks) or along the film edge (e.g., Sony.TM. Dynamic Digital Sound soundtracks). U.S. Pat. Nos. 4,600,280 and 4,461,552, e.g., disclose methods in which digital audio is photographically recorded on motion picture film. U.S. Pat. No. 4,553,833 discloses a method for photographic recording of characters and symbols wherein a light emitting diode array is focused through converging lenses to focus small dot patterns on the film. European Patent Publication EP 0 574 239 discloses method and apparatus for photographically recording digital audio signals with error correction capability on more than one channel. European Patent Publication EP 0 574 136 discloses method and apparatus for recording digital information for clocking tracking error detection and correction, digital audio multichannel tracks and analog audio on a film media.
While digital soundtracks offer the advantage of high quality digital sound recording, they require the use of special sound decoding equipment during projection which all movie theaters may not have. Accordingly, conventional analog soundtracks are typically also included on a motion picture print film which is printed with a digital soundtrack so that such print film may be distributed to theaters which do not have equipment capable of decoding the digital soundtrack as well as those that do. Also, as digital soundtracks record information in the form of very small data bits, they may suffer from poor encoding and recording efficiency associated with the high precision demands of the recording process, as well as data loss due to scratches, etc. While various error detection and correction methods have been proposed for such digital soundtracks, analog soundtracks are still nevertheless desirably included on the print films as backups for the digital soundtracks during projection of a film.
In order to optimize the visual quality of the motion picture image as well as the sound quality of the soundtrack recorded on a motion picture print film, the motion picture and soundtrack are first typically captured or recorded on separate photosensitive films as negative images, and the resulting negatives are then printed in synchronization on the motion picture print film to form positive images. On account of the very short exposure times which must be given to each separate picture, or frame, in capturing a motion picture image, a camera negative film employing relatively fast silver halide emulsions is typically used to record the motion picture images (e.g., Eastman Color Negative Films). In order to reproduce the wide ranges of colors and tones which may be found in various images, the camera film typically also has a relatively low contrast or gamma. Variable area analog soundtracks and digital soundtracts, however, are best recorded with high contrast, relatively slow speed black and white films (e.g., Eastman Sound Recording Films) in order to generate desired sharp images for the sound recording and minimize background noise generated by relatively high minimum densities typically associated with relatively fast films.
Typical black and white sound recording films designed for recording analog soundtracks comprise a relatively fine grain (e.g., grain size less than 0.35 micron) monodispersed silver halide emulsion, which provides the high contrast (e.g., contrast overall gradient greater than 3.7) desirable for recording the soundtrack with sharp edges. White light sources such as tungsten lamps have conventionally been used to record analog soundtracks. Accordingly, the inate sensitivity of many silver halide emulsions in the blue region of the electromagnetic spectrum (e.g., 380-500 nm) has been sufficient for such white light recording. Where additional speed is desired for white light recording or where emulsions are used which lack sufficient inate sensitivity in the visible light region, sound recording films have been sensitized for analog recording with blue and/or green sensitizing dyes.
Digital soundtrack recording is typically performed by exposing a sound recording film to a modulated coherent radiation light source having a narrow band width, such as a modulated laser beam or light emitting diode or diode array. Sound recording films have been made which are optimally spectrally sensitized to provide a peak sensitivity to match a particular digital recording device, along with providing adequate sensitivity for recording anolog soundtracks with white light sources.
Exposing devices of varying peak wavelength have been proposed for digital recording in the industry. Light sources having narrow band widths within both the green (e.g. 500-600 nm) and red (e.g. 600-750 nm) regions, e.g., have been proposed for recording digital soundtracks. Sound recording films have been previously introduced which have been spectrally sensitized with a green spectral sensitizing dye designed to provide optimal sensitivity for recording with a 580 nm light source (e.g., Eastman Sound Recording Film EXR 2378) or with a red spectral sensitizing dye designed to provide optimal sensitivity for recording with a coherent radiation light source providing peak wavelength of about 670 nm (e.g., Eastman Digital Sound Recording Film 2374). Such films allow for both a particular digital as well as an anolog soundtrack to be recorded on a single sound recording film, which can then be printed on a motion picture print film. However, and in order to record separate digital soundtracks having acceptable densities with each of the previously proposed light sources, it is currently necessary to record such soundtracks on separate sound recording films, and then to print both soundtracks onto the print film from the separate negatives. This is a labor intensive process requiring the use of multiple sound recording films and synchronization of the sound negatives to the motion picture. It would be desirable to be able to record multiple digital soundtracks with light sources having peak wavelengths in the green and red regions on a single sound recording film.